.Net API problem with production credentials

Question

I have wokring with third party api with post method.

when i use staging credential's of thired party api it's working.

but when i use production credentials it's not woking , it's return

"The remote server returned an error: (400) Bad Request error"

error but production credential's woking in postman application fine.

where is actually gong wrong i don't understand.i have provide here

my code please check and help,

Thank's in advance. 

string url = "";

HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);

request.Method = "POST";

string client_id="";

string client_secret = "";

string scope = "";

string grant_type = "";

var postData = "client_id:"+client_id.Trim()+"\r\n";

postData += "client_secret:" + client_secret.Trim() + "\r\n";

postData += "scope:" + scope.Trim() + "\r\n";

postData += "grant_type:"+ grant_type.Trim() +"";

string data = postData; // make sure this is URL encoded

request.ContentType = "application/x-www-form-urlencoded";

using (Stream requestStream = request.GetRequestStream())

using (StreamWriter writer = new StreamWriter(requestStream, Encoding.ASCII))

{

writer.Write(data);

}

HttpWebResponse response = (HttpWebResponse)request.GetResponse();

// careful, non-2xx responses will throw an exception

using (Stream responseStream = response.GetResponseStream())

using (StreamReader reader = new StreamReader(responseStream))

{

string a = reader.ReadToEnd();

}